1. Field of the Invention
The present invention is broadly concerned with magnetic switch devices operable to detect relative movement between first and second members, and as proximity detectors. The switches include a switch assembly for mounting to a first member and an attractive component being either itself the component to be detected or for mounting to the second member. The switch assembly preferably includes first and second spaced switch elements and an electrically conductive body shiftable between a first position in simultaneous contact with the first and second switch elements and a second position out of such simultaneous contact. The first switch element is formed of a magnetically attractive material, while the shiftable body is preferably permanently magnetized. When the first and second members are located so that the attractive component is proximal to the switch assembly, the shiftable body is moved to one of its position by virtue of the magnetic attraction between the body and the attractive component. However, when the members are positioned so that the attractive component is remote from the switch assembly, the body is moved to the other of its positions because of the magnetic attraction between the body and the first switch element. Hence, the body remains in contact with the first switch element when the body is in either of its positions, because of the magnetic attraction between the body and the first switch element. In other embodiments, a magnetic switch may be provided having three or four switch elements.
2. Description of the Prior Art
Prior art security alarm systems often make use of magnetic switches attached to doors and windows and integrated with the system for detecting unauthorized openings. One common type of magnetic switch used in these situations is a so-called reed switch. It has been found that reed switches are subject to unauthorized manipulation through use of an external magnet. Specifically, an intruder can hold a relatively strong magnet adjacent the reed switch which will then be operated (to either, open or close depending on the control scheme). With this accomplished, an intruder can open the door or window without triggering the alarm system.
A number of magnetic switches have been proposed in the past to overcome the inherent deficiencies of reed switches. U.S. Pat. Nos. 5,997,873, 5,530,428, 5,332,992, 5,673,021, 5,880,659, 6,506,987 and 6,603,378 describe switches of this type. These switches typically include a pair of spaced apart switch elements with a shiftable body (e.g., a spherical ball) movable between a first position where the ball is in simultaneous contact with both elements and a second position out of such simultaneous contact. An alarm circuit is operatively coupled with the switch elements so as to detect movement of the body. These switches represent a very significant advance in the art.